This invention relates to a single-wall magnetic domain arrangements and more particularly to detection circuits adapted for use in such arrangements.
The advancements in the single-wall magnetic domain technology in recent years have resulted in the realization of various and numerous data processing, memory, and other applications. The control of domain propagation in a thin film magnetic medium and the novel circuits achieved thereby are wellknown and have been extensively treated in the general and patent literature. The manner in which the domains (or "bubbles", as they are familiarly termed) are initially created in a thin film medium is also wellknown. An external bias field of suitable polarity is applied perpendicularly to the plane of the medium to reduce randomly oriented, elongated domain patterns to the individual, cylindrical, bubble-like domains employable as binary bit representations. Once generated, the domains are propagated from point to point within the medium of a system by arrays of magnetic elements such as the familiar Permalloy chevrons, or "T's" and bars, which are magnetized by an externally generated in-plane rotating magnetic field. This rotating field is frequently employed in a single-wall domain system as the timing basis for controlling the various operations of the system. In one prior art system disclosed in U.S. Pat. No. 3,997,877, issued Dec. 14, 1976, to R. A. Naden, for example, the propagation of domains in a magnetic medium is synchronized by counting the number of rotations of the rotating field to determine the proper instant of transfer of the domains from one point to another in the medium. The same rotating field also functions to control the readout of the domain apparatus which is accomplished in one typical arrangement by propagating a domain from the apparatus along a detector path comprising Permalloy propagation elements to a detection array of elements having magnetoresistive characteristics. The presence of a domain in the array is detected magnetoresistively in that the resistance of the array to a current varies in response to the magnetic flux of the domain. When a domain is propagated to a point under the array, the resistance is changed thereby generating an output signal across the array.
The output signal generated by the presence of a domain under the array is a function of the position of the domain relative to the detection array. The output signal waveform is a function of the domain position under the array, that position in the detector array being determined by the direction of the field at the time of readout. In one typical readout arrangement, a domain generated output signal has an amplitude of approximately 700 microvolts and has a duration of approximately 300 nanoseconds of a rotating field cycle of 2800 nanoseconds. In this typical arrangement, the waveform of the output signal is not specified, only the integral of the voltage over the 300 nanoseconds is determined. Accordingly, in such and other arrangements it becomes important to determine the precise times to begin and terminate the integration period to an accuracy commensurate with the output signal duration, in the foregoing illustrative case, a duration of 300 nanoseconds. The direction of the rotating field which determines the position of a domain in the detector array is not precisely determined in time, however. The rotating drive field is generated by causing two nominally sinusoidal currents to pass through two coils with perpendicular axes which encircle the magnetic medium carrying the domains. In the ideal case, where current waveshapes, physical alignment of the structural elements, winding and wiring dimensions, and the like, are perfect, the angle (direction) of the rotating field vector would be precisely linearly proportional to time. In practice, however, none of these ideal conditions are met. As a result, the time relationship between the timing clock of the system which controls the rotating field circuits and the ultimate output signal of the system is uncertain to a degree comparable to the duration of the output signal. As a result, where, for the foregoing reasons, the arrival time of an output signal at the detector is not precisely determined and, on the other hand, the output strobe is controlled to occur at a fixed time, the reliability of readout of a magnetic domain system may be seriously affected. It is to this problem that the detection circuit of this invention is chiefly directed.